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Being overweight is known to increase the risk of needing a knee replacement, but a new study
finds that knee-replacement surgery might also raise a person’s risk of gaining weight.Researchers,
whose findings appeared in the journal
Arthritis Care & Research, analyzed the medical records of nearly 1,000
knee-replacement surgery patients and found that 30 percent gained 5 percent or more of their body
weight in the five years after surgery.

One possible explanation for the counterintuitive results, experts said, is that if people have
spent years adapting to knee pain by taking it easy, they don’t automatically change their habits
when the pain is reduced.

“Future research should develop weight loss/maintenance interventions, particularly for younger
patients who have lost a substantial amount of weight prior to surgery, as they are most at risk
for substantial post-surgical weight gain,” wrote study leader Daniel Riddle, a professor at
Virginia Commonwealth University.

Riddle’s group used a patient registry from the Mayo Clinic in Rochester, Minn., which collected
information on 917 knee-replacement patients before and after their procedures.

The researchers found that five years after surgery, 30 percent of patients had gained at least
5 percent of their weight at the time of the surgery.In contrast, fewer than 20 percent of those in
a comparison group of similar people who had not had surgery gained equivalent amounts of weight in
the same period.

“After knee replacement, we get them stronger and moving better, but they don’t seem to take
advantage of the functional gains,” said Joseph Zeni, a physical-therapy professor at the
University of Delaware who was not part of the study.

“I think that has to do with the fact that we don’t address the behavioral modifications that
have happened during the course of arthritis before the surgery.”

Riddle’s team said weight gain can lead to “meaningful effects on cardiovascular- and
diabetes-related risk, as well as pain and function.”